The present invention relates generally to electromechanical machinery, and more particularly, to such machinery utilizing a disc-type armature.
Electrical rotating machines, such as motors or generators utilizing disc-type armatures, are well-known in the art. Such machines, utilizing wires conventionally wound in laminated or shingle-lapped fashion on the disc armatures, are frequently unsatisfactory in that the armatures are undesirably bulky and irregular winding arrangements are required. Arrangement of the wires conventionally into a suitable winding pattern usually takes the form of a crossover of wires, thereby resulting in a large air-gap between field members and a consequential reduction of flux in the gap, which lowers the effectiveness of the machine.
To overcome these disadvantages, printed circuit-type machines have been used in which a conductive pattern is etched or printed to form the armature winding. An example of a printed disc armature is disclosed in my earlier U.S. Pat. No. 3,096,455 issued on July 2, 1963. This type of motor provides a number of advantages. For example, such machines exhibit virtually no magnetic flux distortion or eddy current induction. The printed circuit armature machines are further advantageous in that they may include a large number of poles without increasing eddy loss and while increasing the back e.m.f. These machines, however, suffer from the disadvantage that, when fabricating a high-power machine, the necessary increase in thickness of copper winding is difficult to accomplish with customary printed circuit techniques. Furthermore, the limitations of such techniques are such that there is a minimum obtainable separation between turns in the winding which limits the number of turns of wire which can be provided in a given area. In addition, customary etching techniques require thin metal conductors, and this increases the resistance of the armature winding. The combination of relatively few turns in a given area with relatively high armature resistance results, of course, in a machine of relatively low power.
Some disc-type machines employ a single layer of conductor winding to form the armature between an opposing pair of field members, such as shown in British Pat. No. 1,299,057 issued on Dec. 6, 1972, to Kollmorgen Corporation. Such machines are usually characterized by relatively low power and efficiency. U.S. Pat. No. 2,847,589 issued on Aug. 12, 1958, to A. W. Haydon shows another version of a disc-type machine wherein the coils are wound in flat spirals on both sides of an insulated disc. This type of arrangement produces a relatively low power machine due to the small number of coil turns per field pole and the low density of copper winding in relation to gap thickness. Other known arragements can boost the efficiency of small disc-type machines to as high as 75 to 80% by using high-strength alnico or rare earth magnets, but these types of magnets are very costly and increasingly scarce due to shortages in the supply of the constituent elements. High efficiencies of up to 90% may be achieved in large, high-power lamination-type motors, but these motors are typically of the order of several hundred pounds in weight and deliver relatively low power in proportion to their weight.
Another characteristic of conventional disc-type machines has been the use of alternating north and south magnets in the field assembly to provide a corresponding number of field poles in the air gap between an opposing pair of field members. In many cases, this construction results in a substantial amount of flux leakage between adjacent oppositely-polarized magnets, thereby reducing the effective magnet surface area which can be obtained from an annular magnet of a given diameter.
It has been found, especially in the case of low energy ferrite based magnets, that the flux density at the poles of a magnet does not increase substantially when the thickness of the magnet is increased beyond a certain point (approximately 1/4" to 3/8" in ferrite magnets). After this point is reached, the only practical way to obtain more flux from the magnet is to increase the surface area of the pole. In the case of disc-type machines, this requires a larger diameter with a larger housing, thus presenting an upper limit to the efficiency of such machines with a given diameter. Furthermore, since the amount of flux leakage in a field assembly of alternating north/south pole construction increases with the number of poles, the diameter of such a machine further limits the number of poles which can effectively be used in the field assembly, resulting in lower induced e.m.f. in the armature coils and reduced efficiency.
U.S. Pat. No. 3,906,267 to Coupin et al, issued on Sept. 16, 1975, describes a machine which relieves some of these flux leakage problems by positioning a high strength, cylindrical, axially magnetized Alnico or rare earth magnet between two ferromagnetic side "cheeks", each having a number of teeth of like polarity. The teeth of each cheek extend radially outwardly from the ends of the magnet and are juxtaposed to the teeth from the other cheek, forming an annular air gap normal to the machine axis and encircling the cylindrical surface of the magnet, in which a stationary disc armature is positioned. The regions of the gap between pairs of aligned teeth thus have high concentrations of magnetic flux density, all with the same polarity, while the intermediate regions of the gap have relatively low flux density. The transition from a maximum extreme to a minimum extreme of flux density produces substantially the same effect as the transition from a north pole to a south pole in a conventional field assembly, while alleviating the problem of flux leakage between adjacent north and south poles. As an armature coil is moved through the gap, an e.m.f. is induced in the coil due to the changing flux density, although the direction of magnetic flux passing through the armature remains constant.
However, the field assembly in Coupin has a number of disadvantages which limit its potential usefulness especially with commonly available low-energy magnets of reasonable cost, such as barium or strontium ferrite. While these magnets may provide a sufficient field for such a machine to operate, the field strength in the air gap would be very low since the magnet's polar surface area is much smaller than the housing size. Thus, for a given machine size, the Coupin design would be impractical to use with low energy magnets, which are much less expensive and more readily available than the high-energy magnets used in Coupin.
Another factor which limits the field strength in Coupin is the presence of stray flux lines in between adjacent regions of high flux density in the gap. Since the e.m.f. induced in a coil is a function of the rate of change of flux lines through the coil, the greatest e.m.f. will be induced when the magnetic field between adjacent regions of high flux density falls as close to zero as possible. Thus, the efficiency of a machine having a uniform polarity magnetic field would be enhanced by a field assembly which is designed to substantially eliminate stray flux lines in between high flux density regions of the gap.
It is, therefore, an important object of the present invention to provide an improved electromechanical machine in which the drawbacks and disadvantages mentioned above are avoided or minimized.
It is a further object of the invention to provide such a machine characterized by low weight, high power, and high efficiency, which may be of the order of 90% or greater.
It is yet another object of this invention to provide an electromechanical machine which is characterized by substantially negligible distortion in its magnetic field and eddy losses, and zero induction in the coils when shorted upon alignment with the stator poles, whereby a machine of high speed, power, and efficiency is attainable.
It is still another object of the invention to provide an electromechanical machine having a coreless disc-type rotor in which the armature coils on one face of the rotor are offset from and connected in a simple manner with the coils on the other face, the coils of the two faces being connected to a commutator such that the machine has high efficiency, smooth torque characteristics, and long brush life.
It is yet a further object of the invention to provide a field assembly for a disc-type electromechanical machine which provides increased field strength for a given diameter housing.
It is a further object to provide such a field assembly which substantially eliminates flux leakage between adjacent poles.
It is still another object to provide such a field assembly which may be advantageously constructed with low-cost ferrite-based magnets.
It is yet another object to provide a field assembly utilizing a uniform polarity magnet structure in which stray flux in the air gap is substantially eliminated.